使用明确的 PID 作为 jstack 的参数来获取 thread dumps。

[user@linux ~]$ jstack -f 5824 

使用 jVisualVM 生成 Thread Dump

通过使用一个程序 jVisuaLVM 来生成 Thread Dump。

如上图在左侧的任务表示当前正在运行的进程列表，点击你想要信息的那个线程，然后选择 thread tab 页来检查实时的线程信息。点击右边的 Thread Dump 按钮来获取 thread dump 文件。

在 Linux 控制台生成

通过使用 ps -ef 命令来获取当前正在运行的 JAVA 应用程序的进程 ID。

[user@linux ~]$ ps - ef | grep java user      2477          1    0 Dec23 ?         00:10:45 ... user    25780 25361   0 15:02 pts/3    00:00:02 ./jstatd -J -Djava.security.policy=jstatd.all.policy -p 2999 user    26335 25361   0 15:49 pts/3    00:00:00 grep java 

使用精确的 pid 作为 kill –SIGQUIT(3) 的参数来获取 thread dump。

Thread Dump 文件的 线程信息

"pool-1-thread-13" prio=6 tid=0x000000000729a000 nid=0x2fb4 runnable [0x0000000007f0f000] java.lang.Thread.State: RUNNABLE               at java.net.SocketInputStream.socketRead0(Native Method)                at java.net.SocketInputStream.read(SocketInputStream.java:129)                at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:264)                at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:306)                at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:158)                - locked <0x0000000780b7e688> (a java.io.InputStreamReader)                at java.io.InputStreamReader.read(InputStreamReader.java:167)                at java.io.BufferedReader.fill(BufferedReader.java:136)                at java.io.BufferedReader.readLine(BufferedReader.java:299)                - locked <0x0000000780b7e688> (a java.io.InputStreamReader)                at java.io.BufferedReader.readLine(BufferedReader.java:362) 

• 线程名字：当使用 Java.lang.Thread 类生成一个线程的时候，该线程将被命名为 Thread-(Number)。但是当使用 java.util.concurrent.ThreadFactory 类的时候，它将被命名为 pool-(number)-thread-(number)。
• 优先级：代表该线程的优先级
• 线程 ID：代表该线程的唯一 ID，（一些有用的信息，比如该线程的 CPU 使用率或者是内存使用率，都能通过该线程 ID 获取到）。
• 线程状态：代表该线程当前的状态
• 线程调用栈：代表该线程的调用栈信息

Thread Dump Patterns by Type When Unable to OBTain a Lock (BLOCKED)

这个应用程序的整体性能下降是因为一个线程占用了锁阻止了其他线程获得锁，在下面的示例中，BLOCKED_TEST pool-1-thread-1 线程占用了 <0x0000000780a000b0> 锁，然而 BLOCKED_TEST pool-1-thread-2 和 BLOCKED_TEST pool-1-thread-3 threads 正在等待获取锁。

 "BLOCKED_TEST pool-1-thread-1" prio=6 tid=0x0000000006904800 nid=0x28f4 runnable [0x000000000785f000]    java.lang.Thread.State: RUNNABLE                 at java.io.FileOutputStream.writeBytes(Native Method)                 at java.io.FileOutputStream.write(FileOutputStream.java:282)                 at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65)                 at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:123)                 - locked <0x0000000780a31778> (a java.io.BufferedOutputStream)                 at java.io.PrintStream.write(PrintStream.java:432)                 - locked <0x0000000780a04118> (a java.io.PrintStream)                 at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:202)                 at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:272)                 at sun.nio.cs.StreamEncoder.flushBuffer(StreamEncoder.java:85)                 - locked <0x0000000780a040c0> (a java.io.OutputStreamWriter)                 at java.io.OutputStreamWriter.flushBuffer(OutputStreamWriter.java:168)                 at java.io.PrintStream.newLine(PrintStream.java:496)                 - locked <0x0000000780a04118> (a java.io.PrintStream)                 at java.io.PrintStream.println(PrintStream.java:687)                 - locked <0x0000000780a04118> (a java.io.PrintStream)                 at com.nbp.theplatform.threaddump.ThreadBlockedState.monitorLock(ThreadBlockedState.java:44)                 - locked <0x0000000780a000b0> (a com.nbp.theplatform.threaddump.ThreadBlockedState)                 at com.nbp.theplatform.threaddump.ThreadBlockedState$1.run(ThreadBlockedState.java:7)                 at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)                 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)                 at java.lang.Thread.run(Thread.java:662)     Locked ownable synchronizers:                 - <0x0000000780a31758> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)  "BLOCKED_TEST pool-1-thread-2" prio=6 tid=0x0000000007673800 nid=0x260c waiting for monitor entry [0x0000000008abf000]    java.lang.Thread.State: BLOCKED (on object monitor)                 at com.nbp.theplatform.threaddump.ThreadBlockedState.monitorLock(ThreadBlockedState.java:43)                 - waiting to lock <0x0000000780a000b0> (a com.nbp.theplatform.threaddump.ThreadBlockedState)                 at com.nbp.theplatform.threaddump.ThreadBlockedState$2.run(ThreadBlockedState.java:26)                 at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)                 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)                 at java.lang.Thread.run(Thread.java:662)     Locked ownable synchronizers:                 - <0x0000000780b0c6a0> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)  "BLOCKED_TEST pool-1-thread-3" prio=6 tid=0x00000000074f5800 nid=0x1994 waiting for monitor entry [0x0000000008bbf000]    java.lang.Thread.State: BLOCKED (on object monitor)                 at com.nbp.theplatform.threaddump.ThreadBlockedState.monitorLock(ThreadBlockedState.java:42)                 - waiting to lock <0x0000000780a000b0> (a com.nbp.theplatform.threaddump.ThreadBlockedState)                 at com.nbp.theplatform.threaddump.ThreadBlockedState$3.run(ThreadBlockedState.java:34)                 at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886                 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)                 at java.lang.Thread.run(Thread.java:662)     Locked ownable synchronizers:                 - <0x0000000780b0e1b8> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)  

当在死锁状态

这是当线程 A 需要获取线程 B 的锁来继续它的任务，然而线程 B 也需要获取线程 A 的锁来继续它的任务的时候发生的。在 thread dump 中，你能看到 DEADLOCK_TEST-1 线程持有 0x00000007d58f5e48 锁，并且尝试获取 0x00000007d58f5e60 锁。你也能看到 DEADLOCK_TEST-2 线程持有 0x00000007d58f5e60，并且尝试获取 0x00000007d58f5e78，同时 DEADLOCK_TEST-3 线程持有 0x00000007d58f5e78，并且在尝试获取 0x00000007d58f5e48 锁，如你所见，每个线程都在等待获取另外一个线程的锁，这状态将不会被改变直到一个线程丢弃了它的锁。

"DEADLOCK_TEST-1" daemon prio=6 tid=0x000000000690f800 nid=0x1820 waiting for monitor entry [0x000000000805f000]    java.lang.Thread.State: BLOCKED (on object monitor)                 at com.nbp.theplatform.threaddump.ThreadDeadLockState$DeadlockThread.goMonitorDeadlock(ThreadDeadLockState.java:197)                 - waiting to lock <0x00000007d58f5e60> (a com.nbp.theplatform.threaddump.ThreadDeadLockState$Monitor)                 at com.nbp.theplatform.threaddump.ThreadDeadLockState$DeadlockThread.monitorOurLock(ThreadDeadLockState.java:182)                 - locked <0x00000007d58f5e48> (a com.nbp.theplatform.threaddump.ThreadDeadLockState$Monitor)                 at com.nbp.theplatform.threaddump.ThreadDeadLockState$DeadlockThread.run(ThreadDeadLockState.java:135)     Locked ownable synchronizers:                 - None  "DEADLOCK_TEST-2" daemon prio=6 tid=0x0000000006858800 nid=0x17b8 waiting for monitor entry [0x000000000815f000]    java.lang.Thread.State: BLOCKED (on object monitor)                 at com.nbp.theplatform.threaddump.ThreadDeadLockState$DeadlockThread.goMonitorDeadlock(ThreadDeadLockState.java:197)                 - waiting to lock <0x00000007d58f5e78> (a com.nbp.theplatform.threaddump.ThreadDeadLockState$Monitor)                 at com.nbp.theplatform.threaddump.ThreadDeadLockState$DeadlockThread.monitorOurLock(ThreadDeadLockState.java:182)                 - locked <0x00000007d58f5e60> (a com.nbp.theplatform.threaddump.ThreadDeadLockState$Monitor)                 at com.nbp.theplatform.threaddump.ThreadDeadLockState$DeadlockThread.run(ThreadDeadLockState.java:135)     Locked ownable synchronizers:                 - None  "DEADLOCK_TEST-3" daemon prio=6 tid=0x0000000006859000 nid=0x25dc waiting for monitor entry [0x000000000825f000]    java.lang.Thread.State: BLOCKED (on object monitor)                 at com.nbp.theplatform.threaddump.ThreadDeadLockState$DeadlockThread.goMonitorDeadlock(ThreadDeadLockState.java:197)                 - waiting to lock <0x00000007d58f5e48> (a com.nbp.theplatform.threaddump.ThreadDeadLockState$Monitor)                 at com.nbp.theplatform.threaddump.ThreadDeadLockState$DeadlockThread.monitorOurLock(ThreadDeadLockState.java:182)                 - locked <0x00000007d58f5e78> (a com.nbp.theplatform.threaddump.ThreadDeadLockState$Monitor)                 at com.nbp.theplatform.threaddump.ThreadDeadLockState$DeadlockThread.run(ThreadDeadLockState.java:135)     Locked ownable synchronizers:                 - None 

当持续等待从远处服务器接收消息

该线程是正常的，因为它的状态为 RUNNABLE，尽管如此，当你按照时间顺序排列 Thread Dump，你会发现 socketReadThread 线程正在无限等待读取 socket。

"socketReadThread" prio=6 tid=0x0000000006a0d800 nid=0x1b40 runnable [0x00000000089ef000]    java.lang.Thread.State: RUNNABLE                 at java.net.SocketInputStream.socketRead0(Native Method)                 at java.net.SocketInputStream.read(SocketInputStream.java:129)                 at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:264)                 at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:306)                 at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:158)                 - locked <0x00000007d78a2230> (a java.io.InputStreamReader)                 at sun.nio.cs.StreamDecoder.read0(StreamDecoder.java:107)                 - locked <0x00000007d78a2230> (a java.io.InputStreamReader)                 at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:93)                 at java.io.InputStreamReader.read(InputStreamReader.java:151)                 at com.nbp.theplatform.threaddump.ThreadSocketReadState$1.run(ThreadSocketReadState.java:27)                 at java.lang.Thread.run(Thread.java:662) 

当 Waiting 时

线程保持在 Waiting 状态，在 Thread Dump 中，IoWaitThread 线程保持等待状态来从 LinkedBlockingQueue 接收消息。如果 LinkedBlockingQueue 一直没有消息，该线程的状态将不会改变。

 "IoWaitThread" prio=6 tid=0x0000000007334800 nid=0x2b3c waiting on condition [0x000000000893f000]    java.lang.Thread.State: WAITING (parking)                 at sun.misc.Unsafe.park(Native Method)                 - parking to wait for  <0x00000007d5c45850> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)                 at java.util.concurrent.locks.LockSupport.park(LockSupport.java:156)                 at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1987)                 at java.util.concurrent.LinkedBlockingDeque.takeFirst(LinkedBlockingDeque.java:440)                 at java.util.concurrent.LinkedBlockingDeque.take(LinkedBlockingDeque.java:629)                 at com.nbp.theplatform.threaddump.ThreadIoWaitState$IoWaitHandler2.run(ThreadIoWaitState.java:89)                 at java.lang.Thread.run(Thread.java:662)   

当线程的资源不能正常的被组织

不必要的线程会堆积起来，当线程的资源不能被正常的组织的话，如果这个发送了，建议监控线程组织过程或检查线程终止的条件。

使用 Thread Dump 怎样解决问题

示例1：当 CPU 利用率高的异常

1. 提取获取最高 CPU 使用率的线程。

[user@linux ~]$ ps -mo pid.lwp.stime.time.cpu -C java       PID         LWP          STIME                  TIME        %CPU 10029               -         Dec07          00:02:02           99.5          -       10039        Dec07          00:00:00              0.1          -       10040        Dec07          00:00:00           95.5 

从这个应用中，发现使用 CPU 最高的线程。

获取使用 CPU 最多的轻量级进程（LWP），把它的唯一标示码 (10039) 转换成十六进制 (0x2737)。

1. 然后获取进程的 Thread Dump，检查进程的动作。

通过 PID 10029 来提取应用程序的 Thread Dump，然后通过一个 nid 0x2737 来找到这个线程。

"NioProcessor-2" prio=10 tid=0x0a8d2800 nid=0x2737 runnable [0x49aa5000] java.lang.Thread.State: RUNNABLE                 at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)                 at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:210)                 at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:65)                 at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:69)                 - locked <0x74c52678> (a sun.nio.ch.Util$1)                 - locked <0x74c52668> (a java.util.Collections$UnmodifiableSet)                 - locked <0x74c501b0> (a sun.nio.ch.EPollSelectorImpl)                 at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:80)                 at external.org.apache.mina.transport.socket.nio.NioProcessor.select(NioProcessor.java:65)                 at external.org.apache.mina.common.AbstractPollingIoProcessor$Worker.run(AbstractPollingIoProcessor.java:708)                 at external.org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:51)                 at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)                 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)                 at java.lang.Thread.run(Thread.java:662) 

每个小时的几个时间提取 Thread Dump，然后检查线程的状态来确定问题。

示例2：当进程的性能异常的慢

多次获得 thread dumps 后，找出 BLOCKED 状态的线程列表。

" DB-Processor-13" daemon prio=5 tid=0x003edf98 nid=0xca waiting for monitor entry [0x000000000825f000] java.lang.Thread.State: BLOCKED (on object monitor)                 at beans.ConnectionPool.getConnection(ConnectionPool.java:102)                 - waiting to lock <0xe0375410> (a beans.ConnectionPool)                 at beans.cus.ServiceCnt.getTodayCount(ServiceCnt.java:111)                 at beans.cus.ServiceCnt.insertCount(ServiceCnt.java:43)  "DB-Processor-14" daemon prio=5 tid=0x003edf98 nid=0xca waiting for monitor entry [0x000000000825f020] java.lang.Thread.State: BLOCKED (on object monitor)                 at beans.ConnectionPool.getConnection(ConnectionPool.java:102)                 - waiting to lock <0xe0375410> (a beans.ConnectionPool)                 at beans.cus.ServiceCnt.getTodayCount(ServiceCnt.java:111)                 at beans.cus.ServiceCnt.insertCount(ServiceCnt.java:43)  " DB-Processor-3" daemon prio=5 tid=0x00928248 nid=0x8b waiting for monitor entry [0x000000000825d080] java.lang.Thread.State: RUNNABLE                 at oracle.jdbc.driver.OracleConnection.isClosed(OracleConnection.java:570)                 - waiting to lock <0xe03ba2e0> (a oracle.jdbc.driver.OracleConnection)                 at beans.ConnectionPool.getConnection(ConnectionPool.java:112)                 - locked <0xe0386580> (a java.util.Vector)                 - locked <0xe0375410> (a beans.ConnectionPool)                 at beans.cus.Cue_1700c.GetNationList(Cue_1700c.java:66)                 at org.apache.jsp.cue_1700c_jsp._jspService(cue_1700c_jsp.java:120) 

在多次获取 thread dumps 后，取得 BLOCKED 状态的线程列表。

如果线程是 BLOCKED 的，提取线程尝试获取的相关联的锁。

通过 thread dumps，你能确定线程状态停止在 BLOCKED，因为锁 <0xe0375410> 不能被获取到，这个问题可以通过分析当前夯住的线程的 stack trace 来解决。

使用 DBMS 的时候，为什么以上的范例经常出现再应用程序中，这有两个原因。第一个原因是配置不当。尽管事实是该线程仍然在工作，它们不能展示它们最好的性能，因为 DBCP 的配置文件没有配置正确。如果你多次提取 thread dumps 并且对比它们，你将经常看到被阻塞的线程之前处于不同的状态。

第二个原因是不正常的连接。当与 DBMS 的连接保持在不正常的状态，线程将等待直到超时。在这个例子中，通过多次提取 thread dumps 并对比它们，你会发现与 DBMS 相关的线程仍然在阻塞状态。通过适当改变一些值，比如超时时间，你可以缩短问题发生的时间。

为简单的 Thread Dump 命名线程编码

当使用 java.lang.Thread 对象创建线程的时候，线程被命名为 Thread-(Number) 。当使用 java.util.concurrent.DefaultThreadFactory 对象创建线程的时候，线程被命名为 named pool-(Number)-thread-(Number)。当为应用程序分析成百上千的线程的时候，如果线程依然用它们默认的名字，分析它们将变得非常困难，因为这是非常难以辨别这些线程来分析的。

因此，你被建议开发一个命名线程的规则当一个新线程被创建的时候。

当你使用 java.lang.Thread 创建线程，你可以通过创建参数给该线程定义个约定俗成的名字。

public Thread(Runnable target, String name); public Thread(ThreadGroup group, String name); public Thread(ThreadGroup group, Runnable target, String name); public Thread(ThreadGroup group, Runnable target, String name, long stackSize); 

当你使用 java.util.concurrent.ThreadFactory 创建线程的时候，你可以通过生成你自己的线程工厂来命名它，如果你不需要特别的功能性，你可以使用 MyThreadFactory 作为以下描述：

import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ThreadFactory; import java.util.concurrent.atomic.AtomicInteger;  public class MyThreadFactory implements ThreadFactory {   private static final ConcurrentHashMap<String, AtomicInteger> POOL_NUMBER =                                                        new ConcurrentHashMap<String, AtomicInteger>();   private final ThreadGroup group;   private final AtomicInteger threadNumber = new AtomicInteger(1);   private final String namePrefix;    public MyThreadFactory(String threadPoolName) {        if (threadPoolName == null) {           throw new NullPointerException("threadPoolName");       }             POOL_NUMBER.putIfAbsent(threadPoolName, new AtomicInteger());        SecurityManager securityManager = System.getSecurityManager();       group = (securityManager != null) ? securityManager.getThreadGroup() :                                                     Thread.currentThread().getThreadGroup();        AtomicInteger poolCount = POOL_NUMBER.get(threadPoolName);        if (poolCount == null) {             namePrefix = threadPoolName + " pool-00-thread-";       } else {             namePrefix = threadPoolName + " pool-" + poolCount.getAndIncrement() + "-thread-";       }   }    public Thread newThread(Runnable runnable) {       Thread thread = new Thread(group, runnable, namePrefix + threadNumber.getAndIncrement(), 0);        if (thread.isDaemon()) {             thread.setDaemon(false);       }        if (thread.getPriority() != Thread.NORM_PRIORITY) {             thread.setPriority(Thread.NORM_PRIORITY);       }        return thread;   } } 

使用 MBean 获取更多的细节信息

你可以使用 MBean 来获取 ThreadInfo 对象。你也可以获取更加多通过 thread dumps 不能获取的信息。通过使用 ThreadInfo。

ThreadMXBean mxBean = ManagementFactory.getThreadMXBean(); long[] threadIds = mxBean.getAllThreadIds(); ThreadInfo[] threadInfos =                 mxBean.getThreadInfo(threadIds);  for (ThreadInfo threadInfo : threadInfos) {   System.out.println(       threadInfo.getThreadName());   System.out.println(       threadInfo.getBlockedCount());   System.out.println(       threadInfo.getBlockedTime());   System.out.println(       threadInfo.getWaitedCount());   System.out.println(       threadInfo.getWaitedTime()); } 

你可以使用方法 ThreadInfo 来提取阻塞线程或者是等待线程花费的时间。并利用这一点，你也可以得到那些处于非活动状态的时间异常长的线程列表。

总结

在本文中，我关注的是为开发人员提供了大量的多线程编程经验，本素材可能是常识。对于经验较少的开发人员来说，我觉得我直接跳过 thread dumps，不提供足够的关于 thread activities 的背景知识。这是由于我的知识缺乏，所以我不能很清晰的简洁明了的解释 thread activities。我衷心的希望本文能给很多开发人员提供帮助。